This invention relates to medical devices, and more particularly to an improved blood sampling device which is mountable on a patient""s forearm or other suitable body location, and which incorporates an admixture reservoir and a closed blood sampling cavity in a single housing.
During the care of critically ill patients and those patients undergoing major surgical procedures, it is common practice to insert one or more catheters into blood vessels of the patient""s cardiovascular circulatory system. These catheters are then used to perform continuous direct, invasive blood pressure monitoring, for delivery of medications or nutrients, and for collection of blood samples to be submitted for laboratory analysis.
The medical staff conducting the procedure might obtain such blood samples by connecting a syringe or other aspirating device, and a shutoff valve directly to the proximal end of a catheter lumen, the distal end of which lies in a patent blood vessel or other chamber containing blood within the body.
But since such catheters represent a communication route to the central circulatory system, careful sample site handling procedures and closed system sampling fittings are often used to minimize the chance for transmission of infection to or from the patient during blood sampling from vascular catheters. Research has shown that a reduction in catheter infection rates can be achieved while simultaneously reducing exposure of the caregiver and other third parties to the patients"" blood, simply by reducing the number of times the catheter ports are opened to the external environment during the course of patient care.
Thus, devices have been developed for blood sampling and/or injection of medications into an otherwise closed fluid-filled cavity which is in communication with a catheter lumen. Devices which use a blunt penetration cannula to enter the cavity (see, for example, published PCT Application No. WO 89/06553) are preferred because they greatly reduce the chance of accidental needle stick injury and the resulting potential for transmission of infections to the caregiver.
When it is important to obtain an undiluted blood sample for laboratory analysis, the cavity must generally be purged of medication and/or other fluids being infused through the catheter lumen. To avoid aspirating and discarding the blood/fluid admixture contained in the cavity, in line reservoirs have been developed to pump away and temporarily store the admixture while a sample of pure blood is drawn off from the cavity (see, for example, U.S. Pat. No. 5,135,489). After the sample is obtained, the reservoir is emptied, returning the admixture to the cavity and catheter, where it is subsequently returned to the patient""s bloodstream. Such reservoir devices are preferable because they minimize the patients"" blood loss, while reducing the creation of biological waste in the critical care environment.
However, currently available blood sampling systems are difficult to use. A common mounting location for blood sampling systems is on a patient""s forearm, adjacent a radial artery catheterization site. Two separate devices, a blood sampling cavity, and an admixture storage reservoir, must be placed in series in the tubing connected to the catheter, running along the patients"" forearm. A practically sized reservoir to aspirate enough admixture to obtain a clean blood sample is sufficiently large that the reservoir is often taped or strapped to the forearm.
Thus, the second device, the blood sampling cavity, is often allowed to flop around freely, juxtapositioned between the reservoir and the proximal end of the catheter. However, since it is unsecured, the chances of accidental contact between the split septum surface of the blood sampling device, the patient""s skin, and other contaminating objects is ever present. And because the cavity is unsecured, it has been considered necessary to develop locking mechanisms to firmly attach the blunt cannula to the cavity (see for example U.S. Pat. No. 5,797,897) during the blood sampling procedure.
In known prior art devices, when a caregiver wishes to use the admixture storage reservoir to remove admixture from the cavity, an actuator device on the reservoir must be pulled away from the reservoir and/or patient""s arm, possibly causing patient discomfort. Even when the reservoir is empty, the protruding actuator lies above the reservoir, creating the potential that the actuator may become entangled in other tubing, electrocardiogram lead wires, or the patient""s clothing.
In some other prior art devices, the reservoir has been moved to a mounting plate disposed on an intravenous (IV) pole adjacent to the patient""s bed to avoid the above mentioned difficulties. However, since the blood sampling cavity must still be located close to the end of the catheter on the patient""s forearm to obtain clean blood samples with reasonably sized admixture reservoirs, these two devices, which must both be manipulated during a blood sampling procedure, are separated by a distance of at least several feet; thus increasing the difficulty of the sampling procedure, and the chance for procedural errors.
Also, in state-of-the-art blood sampling devices, there is always the possibility for formation of small blood clots on the interior walls of the reservoir during sampling, depending variably on the mixture of blood and other fluids that have been pumped from the catheter and the blood sampling cavity. Unfortunately, prior art devices do not contain any active means to ensure that all blood and fluid is urged from the walls of the reservoir after each blood sampling procedure. Thus a thin layer of clotted blood on the reservoir walls can build up with repeated use.
To make the blood sampling procedure as quick and safe as possible for the caregiver and the patient, there is, therefore, a need for an improved blood sampling device which is easily mounted to a patient""s forearm or other body location, without protruding actuator mechanisms which might become entangled in the patient""s clothes or other cables and tubes which may be positioned in close proximity to the patient.
There is a further need for a more secure mounting of the blood sampling cavity to reduce the chance for contamination of the split septum surface which is to be penetrated by the blunt cannula, and to reduce the need for a locking device to secure the blunt cannula.
Further, there is a need for an arm-mounted blood sampling device with an improved actuator which does not require the care giver to pull the actuator in a direction away from the body of the reservoir.
It would also be highly desirable to develop a compact blood sampling device which can be comfortably worn on a patient""s forearm, incorporates all required components in one low cost assembly housing with a minimum number of parts, and which occupies a minimum vertical height when the reservoir is empty, while also elevating and securing the position of the blood sampling cavity and split septum sampling site above the forearm for easier access by the caregiver during the blood sampling procedure.
Finally, it would be highly desirable to provide an admixture reservoir with minimal deadspace volume when closed and an active means to urge any remaining fluid or platelets from the internal walls of the reservoir, such that they might be fully returned to the catheter and cavity when the reservoir is closed.
In accordance with the present invention, an improved blood sampling device is provided for mounting on a patient""s forearm or other suitable body location, which incorporates an admixture reservoir and a closed blood sampling cavity in a single housing, the functional elements of which are firmly mounted and easily accessible to the caregiver. The blood sampling cavity is preferably accessed by a blunt cannula, which is readily retained in the sampling cavity by virtue of the cavity""s secured position and elevated location on the sampling device housing during the sampling procedure, without the need for a cannula locking device. The sampling device of the present invention incorporates an admixture reservoir having a rotary actuator, through which the internal fluid volume of the admixture reservoir is manipulated from nil to a volume which is sufficient to remove all admixture from the blood sampling cavity during a sampling procedure, thus insuring that a clean blood sample may be withdrawn by an aspiration device attached to a sterile blunt cannula which penetrates a split septum of the blood sampling cavity. In a preferred embodiment, the internal surface of the admixture reservoir, which contacts a flexible stopper portion of the actuator, is provided with a curved shape which causes the outer edges of the flexible stopper to first contact the reservoir walls, followed subsequently by wall contact with increasingly more central interior portions of the stopper, and finally through contact and sealing of a central exit port in the reservoir, such that all admixture is urged from the walls of the reservoir as the reservoir is closed.
More particularly, in one aspect of the invention, a blood sampling device is provided, which has a fluid flow path extending therethrough. The fluid flow path has a proximal end and a distal end, the proximal end being adapted for communication with a fluid supply and the distal end being adapted for communication with a catheter placed in a blood vessel. The blood sampling device comprises a fluid storage reservoir having interior walls which define a variable volume, which volume is variable between substantially nil and a maximum volume. An aperture is disposed between the fluid flow path and the fluid storage reservoir, for permitting fluid communication between the fluid flow path and the fluid storage reservoir. A blood sampling cavity is disposed in the blood sampling device, and a split septum is disposed on a wall defining the blood sampling cavity, for sealingly engaging a blunt cannula for the purpose of aspirating blood from the blood sampling cavity.
In another aspect of the invention, there is provided a blood sampling device which has a fluid flow path extending therethrough. The fluid flow path has a proximal end and a distal end, the proximal end being adapted for communication with a fluid supply and the distal end being adapted for communication with a catheter placed in a blood vessel. The blood sampling device comprises a housing, in which the fluid flow path is disposed, and a fluid storage reservoir having a variable volume, which is also disposed in the housing. The reservoir volume is variable between substantially nil and a maximum volume. An actuator is provided for varying the volume of the fluid storage reservoir. Advantageously, an external dimension, preferably height, of the blood sampling device varies in proportion to the variance of the volume of the fluid storage reservoir, such that the external dimension is at a substantial maximum when the volume of the reservoir is at its maximum volume, and at a substantial minimum when the volume of the reservoir is substantially nil. This ability is accomplished by the use of a rotary actuator for varying the volume, which does not extend below the housing when rotated to its most advanced position, corresponding to nil volume, thereby avoiding potential entanglements with clothing, fluid lines, and the like, and does extend below the housing when rotated to a retracted position, corresponding to a substantial volume. When extended, the actuator acts against an adjacent supporting structure, such as a wrist strap, to elevate the split septum and associated blood sampling cavity on the blood sampling device above any adjacent device mounting surface or securement means, so that access to the split septum is eased for the procurement of a blood sample.
In still another aspect of the invention, a blood sampling device is provided, which comprises a fluid flow path extending therethrough. The fluid flow path has a proximal end and a distal end, the proximal end being adapted for communication with a fluid supply and the distal end being adapted for communication with a catheter placed in a blood vessel. A fluid storage reservoir is provided which has interior walls defining a variable volume, which volume is variable between a predetermined minimum volume and a predetermined maximum volume. An aperture is disposed between the fluid flow path and the fluid storage reservoir, for permitting fluid communication between the fluid flow path and the fluid storage reservoir. A movable stopper is disposed in the reservoir for varying the volume. Importantly, one of the interior wall and the movable stopper is flexible in order to actively urge all fluid and blood from the volume after a blood sampling procedure. In the preferred embodiment, it is the stopper which is flexible.
In still another aspect of the invention, a blood sampling device is provided, which has a fluid flow path extending therethrough. The fluid flow path has a proximal end and a distal end, the proximal end being adapted for communication with a fluid supply and the distal end being adapted for communication with a catheter placed in a blood vessel. A fluid storage reservoir is disposed in the device, having an interior wall which defines a volume for containing fluid, which volume is variable between a predetermined minimum volume and a predetermined maximum volume. An aperture is disposed between the fluid flow path and the fluid storage reservoir, for permitting fluid communication between the fluid flow path and the fluid storage reservoir. A movable stopper is disposed in the reservoir for varying the volume. Advantageously, upper portions of the reservoir interior wall adjacent to the aperture are curved in order to actively encourage evacuation of all fluids from the reservoir.
In still another aspect of the invention, a system for invasive pressure monitoring of a patient is provided, which uses direct radial arterial cannulation. The system comprises a blood pressure transducer adapted for disposition on an upper portion of a patient""s arm, and a blood sampling device. The blood sampling device has a fluid flow path extending therethrough. The fluid flow path has a proximal end and a distal end, the proximal end being adapted for communication with a pressure monitoring line which also communicates with a distal port on the blood pressure transducer. The distal end is adapted for communication with a catheter placed in a blood vessel. The blood sampling device comprises a fluid storage reservoir having interior walls which define a variable volume, which volume is variable between substantially nil and a maximum volume. An aperture is disposed between the fluid flow path and the fluid storage reservoir, for permitting fluid communication between the fluid flow path and the fluid storage reservoir. A blood sampling cavity is disposed in the blood sampling device, and a split septum is disposed on a wall defining the blood sampling cavity, for sealingly engaging a blunt cannula for the purpose of aspirating blood from the blood sampling cavity.
In another aspect of the invention, there is disclosed a method for sampling the blood of a patient using a radial artery catheter which has been inserted into an artery of the patient. The method comprises first the step of interrupting any fluid which is being infused into the patient through a fluid line which is attached to the catheter. Then, a volume of a fluid storage reservoir which is contained in a blood sampling device which is disposed in the fluid line is increased from a substantially nil volume to a greater volume, wherein a blood sampling cavity is in fluid communication with the fluid line, and the fluid storage reservoir is in fluid communication with the blood sampling cavity, so that any fluid admixture contained in the blood sampling cavity flows into the fluid storage reservoir. This step of increasing the volume also functions to raise a height of a housing containing the fluid storage reservoir and the blood sampling cavity, thereby raising a height of a split septum disposed on the housing. Following this, a distal end of a cannula is inserted into the split septum, and blood is withdrawn from the blood sampling cavity through the cannula into a syringe attached to a proximal end of the cannula. Following this, the volume of the fluid storage reservoir is decreased and the cannula is removed from the split septum.
An improved and easier to use blood sampling procedure for use with the present invention, which maintains a closed blood sampling system for mutual protection of the patient and caregiver is described.
The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying illustrative drawing.